The answer, in a nutshell, is implicit bias, and specifically “in-group favoritism.” Let me explain. First of all clearly there are a minority of people who have firmly set beliefs that white people are superior to members of other races and/or that men are superior to women and/or that straight people are superior to LGBT folks. These people are angry. They feel like the world they would like to live in is being taken away from them. Some belong to the KKK or other white supremacy groups or identify with them. However these people alone could not have elected Donald Trump as the president of the United States. There just simply are not enough of them. They did not elect Trump.
There are many millions of people however who have unconscious or implicit biases against people of color, against women, against disabled people, against poor people, against GBLT folks, against those who receive governmental assistance. I have no conscious racist beliefs or attitudes. However when I took the Implicit Attitude Test (IAT) on race I discovered to my dismay that I have a strong bias toward white faces rather than black faces. See https://implicit.harvard.edu/implicit/takeatest.html. I am not alone in this and many people of color also have the implicit biases in favor of white over black. These biases are part of our shadows and have developed due to cultural influences throughout our lives, and by definition are outside our awarenesses.
The primary reason that the pollsters got it wrong in this election is due to these powerful unconscious biases and the very strong hard-wired desire that humans have to favor those who we identify as in our camp, our tribe, our group. Fox News and the many fake news outlets contributed significantly to this. President Obama once said that if he watched Fox News he wouldn’t vote for himself. Being exposed to these narratives that President Obama is not a Christian, that Hillary Clinton is a criminal, that they want to take your guns away, etc. etc. quickly amplify the unconscious biases. So even if a person realizes consciously that some of these narratives are not true, the power of them cooking beneath the surface goes on unabated. So then, many people walked into the voting booth and pulled the lever for Trump.
In order to not be adversely affected by these implicit biases, it is necessary to work hard at staying aware of decisions we make and catching ourselves when we make decisions that could be influenced by them. This is not an easy task and requires motivation and commitment. It also means that absent this awareness, commitment and motivation, it is not possible to talk people out of their support for Trump. To challenge their deeply held beliefs even when they are based on inaccurate information that can be verified, will only increase their support of Trump. I believe that Trump will not bring jobs to the coal country; he will not force companies to create jobs; he will not make the lives of working class people better; he will take away health insurance from many who supported him. However when these things happen, I am not optimistic that his supporters will blame Trump. Rather they will blame the Democrats, or the Republicans, or the bureaucrats in Washington, or the liberals, anyone but Trump.